Photoresponse of the Vertebrate Sphincter Pupillae

许多脊椎动物的虹膜上的平滑肌括约肌在受到可见光照射时收缩。它们通过像视紫红质的吸收光谱一样的作用谱来完成这一过程，视紫红质是视网膜杆状色素。这不是由神经元件或细胞膜上的任何电事件介导的。我们建议确定肌细胞中是否含有视紫红质以及其他各种被怀疑参与光导和平滑肌收缩调节的蛋白质，包括：转导蛋白、一种杆状蛋白和平滑肌收缩器中常见的三种蛋白质；钙调蛋白，肌球蛋白轻链激酶和肌球蛋白。对被认为涉及的生化反应的数学描述已经推导出来，本项目建议通过各种细胞生理技术来测试理论的预测。这些措施包括使细胞对分子具有很强的渗透性，否则分子就无法通过细胞膜。这样，分子的浓度就可以通过实验来确定。另一种技术是通过强光闪光从可光性复合物中释放生物活性化合物。光对青蛙虹膜肌的直接激活涉及一系列生化反应，其中光色素的漂白与基于肌动蛋白-肌球蛋白系统的平滑肌收缩相结合。这些生化反应涉及多种细胞类型的信号转导。因此，对这一独特系统的进一步研究可能会为一般的信号转导机制提供新的思路。

The smooth muscle sphincters of the irises of many vertebrate species contract when visible light is shined on them. They do so with an action spectrum like the absorption spectrum of rhodopsin, the retinal rod pigment. This is not mediated by neural elements or even any electrical event at the cell membrane. It is proposed to determine whether the myocytes contain rhodopsin as well as various other proteins suspected of being involved, in phototransduction and regulation of smooth muscle contraction including: transducin, a rod protein, and three proteins commonly found in the contractile apparatus of smooth muscle; calmodulin, myosin light chain kinase and myosin. A mathematical description of the biochemical reactions thought to be involved has been derived and this project proposes to test the predictions of the theory by a variety of cellular physiological techniques. These would include making the cells very permeable to molecules which otherwise would not pass the cell membrane. In this way the concentrations of molecules can be set experimentally. Another technique to be used is to release biologically active compounds from photolabile complexes by strong flashes of light. The direct activation of the frog iris muscle by light involves a combination of biochemical reactions that couple the bleaching of a photopigment to contraction of the smooth muscle by an actin-myosin based system. These biochemical reactions are involved in signal transduction in a variety of cell types. Thus, further study of this unique system may shed new light on signal transduction mechanisms in general.